Field of the Invention
The invention relates to a method for level measurement according to the propagation time method, at least one conductor unit being supplied with pulse-like electromagnetic transmission signals and electromagnetic response signals being tapped from the conductor unit. Furthermore the invention relates to a device for level measurement according to the propagation time method with at least one conductor unit, with at least one electronic device for supplying the conductor unit with pulse-like electromagnetic transmission signals and for tapping of electromagnetic response signals from the conductor unit, and with at least one evaluation device for evaluation of the response signals.
Description of Related Art
In a level measurement device which works according to the propagation time method the so-called TDR measurement principle (time domain reflectometry) is used by the propagation time of electromagnetic signals which have been routed along a conductor unit being evaluated. The conductor unit consists for example of an electrically conductive cable, of a coaxial line, of two adjacent conductors or of at least one conductive bar. The transmission signals are emitted along the conductor unit in the direction of the surface of the medium whose level is to be determined. When the signals strike the surface of the medium, they are in part reflected there. The level of the medium can be determined from the time between the emission and the reception of the reflected response signals. The major advantage of guiding the microwave signals is that changing ambient conditions (for example, a rising or a falling ambient pressure, rising or falling temperature) do not adversely affect the measurement accuracy and that moreover the propagation time of the signal is essentially independent of the dielectric constant of the medium.
The transmission signals are often individual pulses (see, for example, U.S. Pat. No. 6,662,648 B2 or U.S. Pat. No. 7,477,059 B2) which have a positive or negative polarity depending on the sign of the amplitude of the pulse (see for example U.S. Patent Application Publication 2008/0309547 A1).
In order to improve the evaluation of the response signals, providing mechanical reference reflectors along the conductor unit is disclosed for example in U.S. Pat. No. 7,525,476 B1 or U.S. Pat. No. 9,069,056 B2.